Co2 adsorption system and co2 adsorption method

Abstract

To provide a CO2 adsorption system which can be downsized, and can be suppressed in a decline in a CO2 adsorption amount due to zeolite, although moisture is not removed from CO2-containing gas as pretreatment, in cases where CO2 partial pressure in the CO2-containing gas is low, and to provide a CO2 adsorption method.SOLUTION: A CO2 adsorption system 10 is provided, comprising: adsorption towers 21, 22 filled with zeolite; a CO2-containing gas supply line 31 supplying CO2-containing gas G1 to the adsorption towers 21, 22; a compressor 41 provided in the CO2-containing gas supply line 31; a product gas extracting line 32 extracting product gas G2 from the CO2-containing gas G1; and a pressure control section 72 controlling the compressor 41 in such a manner that CO2 partial pressure in the CO2-containing gas G1 becomes 0.001 kPa or more and less than 100kPa. In the adsorption system, a moisture adsorption rate of zeolite is 5 wt.% in an environment of temperature 25°C and relative water vapor pressure 0.5.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a CO2 adsorption system and a CO2 adsorption method. [Background technology]

[0002] In recent years, CO2 capture technology has been attracting attention from the perspective of carbon neutrality and as a countermeasure against the novel coronavirus. Currently, CO2 adsorption systems using adsorption towers filled with zeolite are being developed, but because zeolite easily adsorbs moisture, if the CO2-containing gas supplied to the adsorption tower contains moisture, the zeolite may adsorb the moisture and reduce the amount of CO2 adsorbed.

[0003] For this reason, in order to suppress moisture adsorption by zeolite, moisture is removed from the CO2-containing gas as a pretreatment before supplying the CO2-containing gas to the zeolite. However, a dehumidifier is required to remove the CO2-containing gas as a pretreatment, which results in a large system.

[0004] Meanwhile, a technology has been developed for separating CO2 by using a high-pressure gas containing CO2 and having a CO2 partial pressure of 100 to 4000 kPa, and by using pure silica zeolite as the zeolite, thereby suppressing water adsorption (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5186410 Summary of the Invention [Problem to be solved by the invention]

[0006] However, as in Patent Document 1, when the CO2 partial pressure in the CO2-containing gas is high, i.e., when the amount of CO2 in the CO2-containing gas is large, CO2 repels moisture and is adsorbed to zeolite, but when the CO2 partial pressure is low, i.e., when the amount of CO2 in the CO2-containing gas is small, the pores of the zeolite are filled with moisture, making it difficult to adsorb. Therefore, when the CO2 partial pressure is low, it is still necessary to remove moisture from the CO2-containing gas as a pretreatment.

[0007] The present invention has been made to solve the above problems. That is, the object of the present invention is to provide a CO2 adsorption system and a CO2 adsorption method that can be made compact and can suppress a decrease in the amount of CO2 adsorbed by zeolite even when the CO2 partial pressure in the CO2-containing gas is low, without removing moisture from the CO2-containing gas as a pretreatment. [Means for solving the problem]

[0008] [1] A CO2 adsorption system that uses zeolite to adsorb CO2 in a CO2-containing gas, comprising: one or more adsorption towers filled with zeolite that adsorbs CO2 in a CO2-containing gas; a CO2-containing gas supply line connected to the adsorption towers and supplying the CO2-containing gas to the adsorption towers; a compressor provided in the CO2-containing gas supply line and pressurizing the CO2-containing gas; a product gas extraction line connected to the adsorption towers and extracting a product gas in which CO2 has been separated from the CO2-containing gas; and a pressure control unit that controls the compressor so that the CO2 partial pressure in the CO2-containing gas is 0.001 kPa or more and less than 100 kPa, wherein the water adsorption rate of the zeolite is 5% by weight or less in an environment of a temperature of 25°C and a relative water vapor pressure of 0.5.

[0009] [2] The CO2 adsorption system described in [1] above, wherein the zeolite does not contain Al or the Si / Al atomic ratio of the zeolite is 50 or more.

[0010] [3] A CO2 adsorption system as described in [1] or [2] above, further comprising an on-off valve interposed in the CO2-containing gas supply line and an on-off valve control unit that controls the on-off valve, wherein the on-off valve control unit controls the on-off valve so that the supply time of the CO2-containing gas is 1 second or more and 120 seconds or less.

[0011] [4] The CO2 adsorption system according to any one of [1] to [3] above, further comprising: a regeneration gas supply line branching off from the product gas extraction line, connected to each of the adsorption towers, and supplying a portion of the product gas as regeneration gas to each of the adsorption towers; a product gas flow rate regulator intervening in the product gas extraction line and regulating the flow rate of the product gas; and a product gas flow rate control unit controlling the product gas flow rate regulator, wherein the product gas flow rate control unit controls the product gas flow rate regulator so that the flow rate ratio of the product gas and the CO2-containing gas extracted from the product gas extraction line downstream of the branch point of the regeneration gas supply line is 1:1.1 to 1:20.

[0012] [5] A CO2 adsorption method for adsorbing CO2 in a CO2-containing gas using zeolite, comprising the steps of: preparing one or more adsorption towers filled with zeolite; supplying a CO2-containing gas having a CO2 partial pressure of 0.001 kPa or more and less than 100 kPa into the adsorption towers, adsorbing and separating the CO2 in the CO2-containing gas using the zeolite, and extracting a product gas from the adsorption towers; wherein the water adsorption rate of the zeolite is 5% by weight or less in an environment of a temperature of 25°C and a relative water vapor pressure of 0.5.

[0013] [6] The CO2 adsorption method described in [5] above, wherein the zeolite does not contain Al or the Si / Al atomic ratio of the zeolite is 50 or more.

[0014] [7] The CO2 adsorption method described in [5] or [6] above, wherein the supply time of the CO2-containing gas is from 1 second to 120 seconds.

[0015] [8] The CO2 adsorption method described in any one of [5] to [7] above, wherein there are two or more adsorption towers, further comprising the steps of supplying a portion of the product gas to each of the adsorption towers as a regeneration gas, and desorbing CO2 from the zeolite in each of the adsorption towers to regenerate the zeolite.

[0016] [9] The CO2 adsorption method described in [8] above, wherein the flow rate ratio of the remainder of the product gas after removing a portion of the product gas as the regeneration gas to the CO2-containing gas is 1:1.1 to 1:20. Effect of the Invention

[0017] The CO2 adsorption system and CO2 adsorption method of the present invention can be made compact, and when the CO2 partial pressure in the CO2-containing gas is low, the decrease in the amount of CO2 adsorption by zeolite can be suppressed without removing moisture from the CO2-containing gas as a pretreatment process. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic configuration diagram of a CO2 adsorption system according to an embodiment. [Diagram 2] FIG. 2 is a schematic diagram showing an operating state of the CO2 adsorption system according to the embodiment. [Diagram 3] FIG. 3 is a schematic diagram showing an operating state of the CO2 adsorption system according to the embodiment. [Figure 4] FIG. 4 is a schematic configuration diagram of another CO2 adsorption system according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, a CO2 adsorption system and a CO2 adsorption method according to an embodiment of the present invention will be described. Fig. 1 is a schematic diagram of a CO2 adsorption system according to this embodiment, Figs. 2 and 3 are schematic diagrams showing the operation state of the CO2 adsorption system according to this embodiment, and Fig. 4 is a schematic diagram of another CO2 adsorption system according to this embodiment.

[0020] <<CO2 Adsorption System>> The CO2 adsorption system 10 shown in FIG. 1 is a system that adsorbs CO2 in a CO2-containing gas using zeolite. Specifically, the CO2 adsorption system 10 is a pressure swing adsorption (PSA) system.

[0021] The CO2 adsorption system 10 includes adsorption towers 21 and 22 filled with zeolite (not shown), a CO2-containing gas supply line 31 connected to the adsorption towers 21 and 22 for supplying the CO2-containing gas G1, a product gas extraction line 32 connected to the adsorption towers 21 and 22 for extracting the product gas G2 from which CO2 has been separated from the CO2-containing gas G1, a regeneration gas supply line 33 branched from the product gas extraction line 32 for supplying a part of the product gas G2 as the regeneration gas G3 to the adsorption towers 21 and 22, an exhaust line 34 connected to the adsorption towers 21 and 22 for exhausting the regeneration gas G3 from the adsorption towers 21 and 22, equalizing lines 35 and 36 connected to the adsorption towers 21 and 22 for equalizing the pressure between the adsorption tower 21 and the adsorption tower 22, a compressor 41 provided in the CO2-containing gas supply line 31 for pressurizing the CO2-containing gas G1, and a control unit 71 for controlling the compressor 41 and the like. Note that there may be one or more adsorption towers, and it is not necessarily required to have two. There may be two or more adsorption towers, or three or more.

[0022] In the CO2-containing gas supply line 31, a CO2 concentration measuring device 42 for measuring the CO2 concentration of the CO2-containing gas G1 flowing through the CO2-containing gas supply line 31, a flow meter 43 for measuring the flow rate of the CO2-containing gas G1, a CO2-containing gas flow rate adjusting unit 44 for adjusting the flow rate of the CO2-containing gas G1, and on-off valves V1 and V2 are interposed.

[0023] In the product gas extraction line 32, a CO2 concentration measuring device 51 for measuring the CO2 concentration of the product gas G2 flowing through the product gas extraction line 32 on the downstream side of the branch point of the regeneration gas supply line 33, a flow meter 52 for measuring the flow rate of the product gas G2, a product gas flow rate adjusting unit 53 for adjusting the flow rate of the product gas G2, and on-off valves V3 and V4 are interposed.

[0024] An on-off valve V5 is provided in the regeneration gas supply line 33. An exhaust line 34 is provided with a CO2 concentration measuring device 61 for measuring the CO2 concentration of exhaust gas G4 flowing through the exhaust line 34, a flowmeter 62 for measuring the flow rate of exhaust gas G4, an exhaust gas flow rate regulator 63 for regulating the flow rate of exhaust gas G4, and on-off valves V6 and V7. An on-off valve V8 is provided in the pressure equalizing line 35, and an on-off valve V9 is provided in the pressure equalizing line 36.

[0025] <Adsorption tower> The adsorption towers 21 and 22 are filled with zeolite. The zeolite has a moisture adsorption rate of 5% by weight or less under an environment of a temperature of 25° C. and a relative water vapor pressure of 0.5. If the moisture adsorption rate is 5% by weight or less, good hydrophobicity can be obtained. The moisture adsorption rate of the zeolite under the above environment is preferably 4.8% by weight or less, 4.5% by weight or less, 4% by weight or less, 3.5% by weight or less, or 3% by weight or less. In this specification, the term "relative water vapor pressure" refers to the ratio (P / P0) of the water vapor pressure (adsorption equilibrium pressure) P (mmHg) in the adsorption equilibrium state to the saturated vapor pressure P0 (mmHg) of water vapor. The moisture adsorption rate can be measured under an environment of 25° C. using a moisture adsorption capacity measuring device (product name "Vstar", manufactured by Anton Paar Co., Ltd.).

[0026] Zeolite having such a water adsorption rate is not particularly limited, but for example, the product name "MFI-S" (MFI type zeolite) manufactured by Z Chemical Co., Ltd. can be mentioned. In addition, even if the water adsorption rate in the above environment exceeds 5% by weight, for example, a zeolite that does not contain Al or has an Si / Al atomic ratio of 50 or more can be contacted with a solution containing fluoride ions to obtain a zeolite with a water adsorption rate of 5% by weight or less in the above environment. When the zeolite does not contain Al or has a high Si / Al atomic ratio, it is predicted that the hydrophobicity will be high and the water will not be attracted. However, in reality, when the zeolite does not contain Al or has a high Si / Ai atomic ratio, there are many defects (silanol defects), and the silanol groups present in the defects adsorb water, so that the zeolite may not be hydrophobic. In addition, when the zeolite does not contain Al or has a high Si / Al ratio, the more defects are likely to occur. Therefore, even if the zeolite does not contain Al or has a high Si / Al atomic ratio, the zeolite may not have a moisture adsorption rate of 5% by weight or less under an environment of a temperature of 25°C and a relative water vapor pressure of 0.5. On the other hand, fluoride ions can break and recombine the Si-O bonds in the zeolite framework. When fluoride ions are brought into contact with the raw zeolite, Si in the zeolite framework migrates, and defects move so that the surface area decreases, so that defects gather and the number of defects decreases. Therefore, when a treatment is performed using a solution containing fluoride ions, the defects are repaired by the action of the fluoride ions, and Si migrates, resulting in a zeolite with fewer defects. This makes it possible to obtain a zeolite with a moisture adsorption rate of 5% by weight or less under the above environment. Note that fluoride ions have the ability to repair defects, but chloride ions and bromide ions do not have the ability to repair defects. This is believed to be because the size of fluoride ions is smaller than the sizes of chloride ions and bromide ions, and therefore they can easily enter zeolite.

[0027] The concentration of fluoride ions in the solution containing fluoride ions is preferably 0.001% by mass or more. If the concentration of fluoride ions is 0.001% by mass or more, the moisture adsorption rate can be effectively reduced under the above-mentioned environment. The lower limit of the concentration of fluoride ions is preferably 0.005% by mass or more, and more preferably 0.01% by mass or more. From the viewpoint of suppressing the collapse of the zeolite structure, the upper limit of the concentration of fluoride ions is more preferably 25% by mass or less, and even more preferably 15% by mass or less.

[0028] The solution containing fluoride ions is not particularly limited, but can be obtained by dissolving a fluoride such as ammonium fluoride, sodium fluoride, potassium fluoride, tetramethylammonium fluoride, tetraethylammonium fluoride, or tetrapropylammonium fluoride in a solvent such as water.

[0029] The solution containing fluoride ions may contain an organic structure directing agent such as tetraethylammonium hydroxide (TEAOH) in addition to fluoride ions and a solvent. By adding an organic structure directing agent to this solution, the organic structure directing agent can fill the pores in the zeolite and stabilize the structure, thereby reducing the water adsorption rate under the above environment. However, the organic structure directing agent does not have to be included in this solution.

[0030] The temperature of the solution containing fluoride ions is not particularly limited as long as it is equal to or higher than 0° C. and lower than 374° C. The lower limit of the temperature of the solution is preferably equal to or higher than 10° C., more preferably equal to or higher than 20° C., and the upper limit of the temperature of the solution is preferably equal to or lower than 250° C., more preferably equal to or lower than 200° C., even more preferably equal to or lower than 150° C., and most preferably equal to or lower than 100° C.

[0031] The treatment of zeolite with a solution containing fluoride ions is not particularly limited, but may be for 10 minutes or more. By carrying out the treatment for 10 minutes or more, the moisture adsorption rate can be reliably reduced. The lower limit of this treatment time is not particularly limited, but is preferably 1 hour or more, and more preferably 3 hours or more. In addition, the upper limit of this treatment time is preferably 72 hours or less, and more preferably 48 hours or less, from the viewpoint of energy consumption.

[0032] It is preferable that the zeolite does not contain Al, or that the Si / Al atomic ratio of the zeolite is 50 or more. Even if the moisture adsorption rate of such a zeolite exceeds 5% by weight under an environment of a temperature of 25° C. and a relative water vapor pressure of 0.5, the moisture adsorption rate under the above environment can be reduced to 5% by weight or less by contacting it with a solution containing fluoride ions. The lower limit of the Si / Al atomic ratio of the zeolite is preferably 75 or more, 85 or more, or 100 or more. The upper limit of the Si / Al atomic ratio of the zeolite may be infinite, but as described above, the higher the Si / Al atomic ratio, the more defects are likely to occur, so it is preferably 2000 or less, 1000 or less, or 500 or less. The Si / Al atomic ratio can be determined by measuring the amounts of Si and Al by inductively coupled plasma emission spectrometry (ICP). The Si / Al atomic ratio of the zeolite is preferably 75 or more and 2,000 or less, more preferably 85 or more and 1,000 or less, and even more preferably 100 or more and 500 or less.

[0033] The type of zeolite is not particularly limited, but for example, one or more zeolites selected from the group consisting of FAU type zeolite (Y type zeolite), MFI type zeolite, MOR type zeolite, and FER type zeolite are preferred. Among these, FAU type zeolite (Y type zeolite) or MFI type zeolite is more preferred from the viewpoint of production cost.

[0034] The average particle size of the zeolite may be 0.005 μm or more and 100 μm or less. The lower limit of the average particle size of the zeolite is preferably 0.007 μm or more, 0.008 μm or more, or 0.01 μm or more, and the upper limit is preferably 90 μm or less, 80 μm or less, or 50 μm or less. If the average particle size of the zeolite is 0.01 μm or more, it can be easily handled, and if it is 50 μm or less, it becomes easier to design the apparatus from the viewpoint of the CO2 adsorption rate.

[0035] The average particle size of the zeolite is measured by observing the zeolite using a field emission scanning electron microscope (model name "JSM-7000F", manufactured by JEOL Ltd.), measuring the horizontal Feret diameters of 30 or more randomly measured particles, and taking the arithmetic mean value as the average particle size.

[0036] The zeolite may be in powder form, but is preferably in pellet form. By using pelletized zeolite, the resistance when the CO2-containing gas diffuses through the zeolite can be reduced compared to the case of using powdered zeolite, so that the adsorption characteristics of CO2 can be improved.

[0037] <CO2-containing gas supply line> The CO2-containing gas supply line 31 is for supplying the CO2-containing gas G1 to the adsorption towers 21 and 22. The side of the CO2-containing gas supply line 31 connected to the adsorption towers 21 and 22 is divided into a supply line 31A connected to the adsorption tower 21 and a supply line 31B connected to the adsorption tower 22. The CO2 concentration in the CO2-containing gas G1 flowing through the CO2-containing gas supply line 31 is not particularly limited, and may be, for example, 100 ppm or more and 200000 ppm or less.

[0038] <Product gas extraction line> The product gas extraction line 32 is for adsorbing and separating CO2 in the CO2-containing gas G1 by the zeolite in the adsorption towers 21, 22, and extracting the product gas G2 from the adsorption towers 21, 22. The product gas extraction line 32 on the adsorption towers 21, 22 side is divided into an extraction line 32A connected to the adsorption tower 21 and an extraction line 32B connected to the adsorption tower 22.

[0039] The CO2 concentration in the product gas G2 flowing through the product gas discharge line 32 is preferably low, for example, 300 ppm or less. The CO2 concentration in the product gas G2 is more preferably 250 ppm or less or 200 ppm or less.

[0040] <Regenerated gas supply line> The regeneration gas supply line 33 is for supplying a portion of the product gas G2 as a regeneration gas G3 to the adsorption towers 21, 22. The regeneration gas supply line 33 is connected to the adsorption towers 21, 22. The regeneration gas G3 flowing through the regeneration gas supply line 33 is separated from the product gas G2, and therefore the CO2 concentration in the regeneration gas G3 is similar to the CO2 concentration in the product gas G2.

[0041] <Exhaust line> The exhaust line 34 is for exhausting the regeneration gas G3 from the adsorption towers 21 and 22. The exhaust line 34 is connected to the adsorption towers 21 and 22. If the CO2 concentration in the exhaust gas G4 is higher than the CO2 concentration in the regeneration gas G3 and the CO2 concentration in the product gas G2, it can be considered that the CO2 adsorbed to the zeolite by the regeneration gas G3 is desorbed. The CO2 concentration in the exhaust gas G4 is preferably 450 ppm or more.

[0042] <Control Unit> The control unit 71 includes a pressure control unit 72 that controls the compressor 41, a CO2-containing gas flow rate control unit 73 that controls the CO2-containing gas flow rate control unit 44, a product gas flow rate control unit 74 that controls the product gas flow rate control unit 53, an exhaust gas flow rate control unit 75 that controls the exhaust gas flow rate control unit 63, and an on-off valve control unit 76 that controls the opening and closing of on-off valves V1 to V9.

[0043] The pressure control unit 72 controls the compressor 41 so that the CO2 partial pressure in the CO2-containing gas G1 is 0.001 kPa or more and less than 100 kPa. This control allows the CO2 partial pressure to be supplied to the adsorption towers 21, 22 at 0.001 kPa or more and less than 100 kPa. The lower limit of the CO2 partial pressure in the CO2-containing gas G1 may be 0.01 kPa or more, 0.03 kPa or more, or 0.04 kPa or more, and the upper limit may be 80 kPa or less, 50 kPa or less, 10 kPa or less, 5 kPa or less, or 1 kPa or less. In this specification, pressure means absolute pressure.

[0044] The pressure of the CO2-containing gas G1 may be 130 kPa or more and 800 kPa or less. If the pressure of the CO2-containing gas G1 is 130 kPa or more, the CO2 adsorption system 10 can be operated, and if the pressure is 800 kPa or less, the CO2 adsorption system 10 can be made smaller, so that the initial cost and running cost can be reduced. The lower limit of the pressure of the CO2-containing gas G1 may be 150 kPa or more, 170 kPa or more, or 200 kPa or more, and the upper limit may be 700 kPa or less, 500 kPa or less, or 300 kPa or less.

[0045] The product gas flow rate control unit 74 or the product gas flow rate control unit 74 and the CO2-containing gas flow rate control unit 73 preferably controls the product gas flow rate adjustment unit 53 or the product gas flow rate adjustment unit 53 and the CO2-containing gas flow rate adjustment unit 44 so that the flow rate ratio of the product gas G2 and the CO2-containing gas G1 taken out from the downstream side of the branch point of the regeneration gas supply line 33 in the product gas take-out line 32 is 1:1.1 to 1:20, preferably 1:1.5 to 1:10 or 1:2 to 1:4. The flow rate ratio of the product gas G2 and the CO2-containing gas G1 is a ratio that affects the optimization of the zeolite and the system cost to be installed, and is also a factor that determines the quality of the product gas G2, so that the operation of the CO2 adsorption system 10 can be optimized by controlling it to such a flow rate ratio.

[0046] The CO2-containing gas flow rate control unit 73 preferably controls the CO2-containing gas flow rate adjustment unit 44 so that the flow rate of the CO2-containing gas G1 is 0.1 L / min or more and 200,000 L / min or less. If the flow rate of the CO2-containing gas G1 is 0.1 L / min or more, flow rate detection can be performed accurately and at low cost, so that it can be controlled with an inexpensive device, and if it is 200,000 L / min or less, it is optimal for the scale of one module of the CO2 adsorption system 10. It is more preferable that the lower limit of the flow rate of the CO2-containing gas G1 is 0.15 L / min or more, 0.2 L / min or more, or 0.3 L / min or more, and the upper limit is 175,000 L / min or less, 150,000 L / min or less, or 100,000 L / min or less.

[0047] The product gas flow rate control unit 74 preferably controls the product gas flow rate adjustment unit 53 so that the flow rate of the product gas G2 extracted from the product gas extraction line 32 downstream of the branch point of the regeneration gas supply line 33 is 0.05 L / min or more and 180,000 L / min or less. If the flow rate of the product gas G2 is 0.05 L / min or more, flow rate detection can be performed accurately and at low cost, so that it can be controlled with an inexpensive device, and if it is 180,000 L / min or less, it is optimal for the scale of one module of the CO2 adsorption system 10. It is more preferable that the lower limit of the flow rate of the product gas G2 is 0.05 L / min or more, 0.07 L / min or more, or 0.1 L / min or more, and the upper limit is 160,000 L / min or less, 110,000 L / min or less, or 70,000 L / min or less.

[0048] The exhaust gas flow rate control unit 75 preferably controls the exhaust gas flow rate adjusting unit 63 so that the flow rate of the exhaust gas G4 is 0.05 L / min or more and 40,000 L / min or less. If the flow rate of the exhaust gas G4 is 0.05 L / min or more, the flow rate can be detected accurately and at low cost, so it can be controlled with an inexpensive device. If it is 40,000 L / min or less, it is optimal as the scale of one module of the CO2 adsorption system 10. The lower limit of the flow rate of the exhaust gas G4 is preferably controlled to be 0.06 L / min or more, 0.07 L / min or more, or 0.1 L / min or more, and the upper limit is preferably controlled to be 30,000 L / min or less, 20,000 L / min or less, or 10,000 L / min or less.

[0049] The on-off valve control unit 76 controls the opening and closing of the on-off valves V1 to V9 according to the procedure described later. It is preferable to control the on-off valves V1 and V2 so that the supply time of the CO2-containing gas G1 per cycle (the adsorption time of CO2 by zeolite) is 1 second or more and 120 seconds or less. If this supply time is 1 second or more, the zeolite can adsorb more CO2 in the CO2-containing gas G1. If it is 120 seconds or less, the device can be designed with the zeolite mounting weight considering the cost of the device. The lower limit of the supply time of the CO2-containing gas G1 per cycle is preferably controlled to be 1.2 seconds or more, 1.5 seconds or more, or 2 seconds or more, and the upper limit is preferably controlled to be 100 seconds or less, 80 seconds or less, or 60 seconds or less.

[0050] <<CO2 Adsorption Method>> The adsorption of CO2 using the CO2 adsorption system 10 shown in FIG. 1 is performed as follows. The adsorption process of the adsorption tower 21 and the regeneration process of the adsorption tower 22 are performed with the on-off valves V1, V3, V5, and V7 open and the on-off valves V2, V4, V6, V8, and V9 closed.

[0051] As shown in FIG. 2, in the adsorption step of the adsorption tower 21, first, a CO2-containing gas G1 having a CO2 partial pressure of 0.001 kPa or more and less than 100 kPa is supplied from the compressor 41 to the adsorption tower 21 through the CO2-containing gas supply line 31 (supply line 31A). The supply time of the CO2-containing gas per cycle is preferably 1 second or more and 120 seconds or less. The CO2-containing gas G1 supplied to the adsorption tower 21 is separated from the CO2-containing gas G1 by adsorbing the CO2 in the CO2-containing gas G1 to the zeolite, thereby generating a product gas G2. The product gas G2 generated in the adsorption tower 21 is extracted through the product gas extraction line 32 (extraction line 32A). A part of the product gas G2 generated in the adsorption tower 21 is supplied to the adsorption tower 22 through the regeneration gas supply line 33 as the regeneration gas G3. The flow rate ratio of the remaining product gas G2 after removing a portion of the product gas G2 as the regeneration gas G3 to the CO2-containing gas G1 is preferably 1:1.1 to 1:20.

[0052] Meanwhile, in the regeneration process of the adsorption tower 22, the CO2-containing gas G1 in the adsorption tower 22 is discharged together with the regeneration gas G3 through the regeneration gas supply line 33 to the outside, which is lower than the pressure inside the adsorption tower 22, due to the pressure difference. As a result, the pressure inside the adsorption tower 22 is reduced, and the CO2 adsorbed on the zeolite is desorbed from the zeolite. The desorbed CO2 is discharged from the adsorption tower 22 together with the CO2-containing gas G1 and the regeneration gas G3 through the exhaust line 34. As a result, the zeolite inside the adsorption tower 22 is regenerated.

[0053] After the adsorption process of the adsorption tower 21 and the regeneration process of the adsorption tower 22 are completed, a pressure equalization process is performed in which the gas in the adsorption tower 21 is transferred to the adsorption tower 22. The pressure equalization process is performed by closing the on-off valves V1, V3, V5, and V7 and opening the on-off valves V8 and V9. In the pressure equalization process, the gas that filled the adsorption tower 21 is transferred to the adsorption tower 22 through the pressure equalization lines 35 and 36.

[0054] After the pressure equalization process is completed, the regeneration process of the adsorption tower 21 and the adsorption process of the adsorption tower 22 are performed. The regeneration process of the adsorption tower 21 and the adsorption process of the adsorption tower 22 are performed with the on-off valves V2, V4, V5, and V6 open and the on-off valves V1, V3, V7, V8, and V9 closed.

[0055] As shown in FIG. 3, in the adsorption step of the adsorption tower 22, first, a CO2-containing gas G1 having a CO2 partial pressure of 0.001 kPa or more and less than 100 kPa is supplied to the adsorption tower 22 through the CO2-containing gas supply line 31 (supply line 31B) by the compressor 41. The supply time of the CO2-containing gas per cycle is preferably 1 second or more and 120 seconds or less. The CO2-containing gas G1 supplied to the adsorption tower 22 is separated from the CO2-containing gas G1 by adsorbing the CO2 in the CO2-containing gas G1 to the zeolite, thereby generating a product gas G2. The product gas G2 generated in the adsorption tower 22 is extracted through the product gas extraction line 32 (extraction line 32B). A part of the product gas G2 generated in the adsorption tower 22 is supplied to the adsorption tower 21 through the regeneration gas supply line 33 as the regeneration gas G3. The flow rate ratio of the remaining product gas G2 after removing a portion of the product gas G2 as the regeneration gas G3 to the CO2-containing gas G1 is preferably 1:1.1 to 1:20.

[0056] Meanwhile, in the regeneration process of the adsorption tower 21, the CO2-containing gas G1 in the adsorption tower 21 is discharged together with the regeneration gas G3 through the regeneration gas supply line 33 to the outside, which is lower than the pressure inside the adsorption tower 21, due to the pressure difference. As a result, the pressure inside the adsorption tower 21 is reduced, and the CO2 adsorbed on the zeolite is desorbed from the zeolite. The desorbed CO2 is discharged from the adsorption tower 21 together with the CO2-containing gas G1 and the regeneration gas G3 through the exhaust line 34. As a result, the zeolite inside the adsorption tower 21 is regenerated.

[0057] After the adsorption process of the adsorption tower 22 and the regeneration process of the adsorption tower 21 are completed, a pressure equalization process is performed in which the gas in the adsorption tower 22 is transferred to the adsorption tower 21. The pressure equalization process is performed by closing the on-off valves V2, V4, V5, and V6 and opening the on-off valves V8 and V9. In the pressure equalization process, the gas that filled the adsorption tower 22 is transferred to the adsorption tower 21 through the pressure equalization lines 35 and 36.

[0058] After the pressure equalization process is completed, the adsorption process of the adsorption tower 21 and the regeneration process of the adsorption tower 22 are performed again. When the adsorption process of the adsorption tower 21, the regeneration process of the adsorption tower 22, and the pressure equalization process are defined as one cycle, and when the adsorption process of the adsorption tower 22, the regeneration process of the adsorption tower 21, and the pressure equalization process are defined as one cycle, the above cycle is repeated in the adsorption towers 21 and 22.

[0059] According to this embodiment, since zeolite with a moisture adsorption rate of 5% by weight or less in an environment of a temperature of 25°C and a relative water vapor pressure of 0.5 is used, when a CO2-containing gas G1 with a CO2 partial pressure of 0.001 kPa or more and less than 100 kPa is supplied, the zeolite is less likely to attract moisture. As a result, CO2 can be adsorbed by the zeolite without removing moisture from the CO2-containing gas as a pretreatment. In addition, since there is no need to remove moisture from the CO2-containing gas as a pretreatment, there is no need to install a dehumidifier, and the size can be reduced.

[0060] In this embodiment, the CO2 adsorption system 10 is a pressure swing adsorption (PSA) system, but the CO2 adsorption system can also be applied to a temperature swing adsorption (TSA) system, a vacuum swing adsorption (VSA) system, or a pressure vacuum swing adsorption (PVSA) system. The CO2 adsorption system 80 shown in FIG. 4 is a pressure vacuum swing adsorption system, and includes a vacuum pump 64 in the exhaust line 34 and a vacuum pump control unit 77 in the control unit 71 for controlling the vacuum pump. In the CO2 adsorption system 80, the on-off valve V7 is opened during the adsorption process of the adsorption tower 21 and the regeneration process of the adsorption tower 22, and the vacuum pump 64 is operated while being controlled by the vacuum pump control unit 77. EXAMPLES

[0061] In order to explain the present invention in detail, examples are given below, but the present invention is not limited to these descriptions.

[0062] <Example 1> Using the CO2 adsorption system 10 shown in Fig. 1, a test was carried out in which CO2 was adsorbed by zeolite in the adsorption towers 21 and 22. Specifically, the following test was carried out.

[0063] First, as the zeolite to be packed in the adsorption towers 21 and 22, pellet-shaped MFI type zeolite (product name "MFI-S", manufactured by Z Chemical Corporation) having a diameter of 1.6 mm and a length of 4 mm to 6 mm was prepared.

[0064] The Si / Al atomic ratio of this zeolite was 300. The Si / Al ratio of the zeolite was determined as follows. Specifically, 50 mg of zeolite was first dissolved in a 2 mol / L potassium hydroxide solution to prepare a sample solution. Then, using an ICP emission spectrometer (device name "iCAP-6300", manufactured by Thermo Fisher Scientific), composition analysis was performed on the sample solution and a separately prepared calibration solution. The Si / Al ratio was determined from the obtained analysis results.

[0065] The moisture adsorption rate of this zeolite was 5% by weight at a temperature of 25°C and a relative water vapor pressure of 0.5. The moisture adsorption rate was measured by reaching equilibrium at a temperature of 25°C and a relative water vapor pressure of 0.5 using a moisture adsorption capacity measuring device (product name "Vstar", manufactured by Anton Paar Co., Ltd.). The moisture adsorption rates of zeolite at a temperature of 25°C and a relative water vapor pressure of 0.5 were measured in the same manner for the other examples and comparative examples.

[0066] Then, 250 g of this zeolite was packed into each of the adsorption towers 21 and 22 without being dried.

[0067] Using the adsorption towers 21 and 22 filled with this zeolite, first, an adsorption step in the adsorption tower 21 and a regeneration step in the adsorption tower 22 were carried out. The adsorption step in the adsorption tower 21 and the regeneration step in the adsorption tower 22 were carried out with the on-off valves V1, V3, V5, and V7 open and the on-off valves V2, V4, V6, V8, and V9 closed.

[0068] In the adsorption step of the adsorption tower 21, first, a CO2-containing gas G1, which is air at 25°C and a relative humidity of 30%, is supplied from the compressor 41 to the adsorption tower 21 through the CO2-containing gas supply line 31 at a flow rate of 20 L / min. The partial pressure of CO2 in the CO2-containing gas G1 was measured to be 0.04 kPa. The supply time of the CO2-containing gas per cycle (cycle time) was set to 12 seconds. In the adsorption tower 21, CO2 in the CO2-containing gas G1 is adsorbed by zeolite, so that CO2 is separated from the CO2-containing gas G1 to generate a product gas G2. The product gas G2 generated in the adsorption tower 21 is taken out through the product gas take-out line 32. A part of the product gas G2 generated in the adsorption tower 21 is supplied to the adsorption tower 22 through the regeneration gas supply line 33 as a regeneration gas G3. The remaining part of the product gas G2 after removing a part of the product gas G2 as the regeneration gas G3 was controlled to be 5 L / min. Therefore, the flow rate ratio of the remaining part of the product gas G2 after removing a part of the product gas G2 as the regeneration gas G3 to the CO2-containing gas G1 was 1:4.

[0069] Meanwhile, in the regeneration process of the adsorption tower 22, the CO2-containing gas G1 in the adsorption tower 22 was discharged together with the regeneration gas G3 through the regeneration gas supply line 33 to the outside, which was lower than the pressure inside the adsorption tower 22, due to the pressure difference. As a result, the pressure inside the adsorption tower 22 was reduced to atmospheric pressure (101.3 kPa), and the CO2 adsorbed on the zeolite was desorbed from the zeolite. The desorbed CO2 was discharged from the adsorption tower 22 together with the CO2-containing gas G1 and the regeneration gas G3 through the exhaust line 34. As a result, the zeolite inside the adsorption tower 22 was regenerated.

[0070] After the adsorption process in the adsorption tower 21 and the regeneration process in the adsorption tower 22 were completed, a pressure equalization process was carried out to transfer the gas in the adsorption tower 21 to the adsorption tower 22. The pressure equalization process was carried out by closing the on-off valves V1, V3, V5, and V7 and opening the on-off valves V8 and V9.

[0071] After the pressure equalization process was completed, the regeneration process of the adsorption tower 21 and the adsorption process of the adsorption tower 22 were carried out. The regeneration process of the adsorption tower 21 and the adsorption process of the adsorption tower 22 were carried out with the on-off valves V2, V4, V5, and V6 open and the on-off valves V1, V3, V7, V8, and V9 closed.

[0072] In the adsorption step of the adsorption tower 22, first, a CO2-containing gas G1, which is air at 25°C and a relative humidity of 30%, is supplied from the compressor 41 to the adsorption tower 22 through the CO2-containing gas supply line 31 at a flow rate of 20 L / min. The partial pressure of CO2 in the CO2-containing gas G1 was measured and found to be 0.04 kPa. The supply time of the CO2-containing gas per cycle (cycle time) was set to 12 seconds. In the adsorption tower 22, CO2 in the CO2-containing gas G1 is adsorbed by zeolite, so that CO2 is separated from the CO2-containing gas G1 to generate a product gas G2. The product gas G2 generated in the adsorption tower 22 is taken out through the product gas take-out line 32. A part of the product gas G2 generated in the adsorption tower 22 is supplied to the adsorption tower 21 through the regeneration gas supply line 33 as a regeneration gas G3. The remaining part of the product gas G2 after removing a part of the product gas G2 as the regeneration gas G3 was controlled to be 5 L / min. Therefore, the flow rate ratio of the remaining part of the product gas G2 after removing a part of the product gas G2 as the regeneration gas G3 to the CO2-containing gas G1 was 1:4.

[0073] Meanwhile, in the regeneration process of the adsorption tower 21, the CO2-containing gas G1 in the adsorption tower 21 was discharged together with the regeneration gas G3 through the regeneration gas supply line 33 to the outside, which was lower than the pressure inside the adsorption tower 21, due to the pressure difference. As a result, the pressure inside the adsorption tower 21 was reduced to atmospheric pressure (101.3 kPa), and the CO2 adsorbed on the zeolite was desorbed from the zeolite. The desorbed CO2 was discharged from the adsorption tower 21 together with the CO2-containing gas G1 and the regeneration gas G3 through the exhaust line 34. As a result, the zeolite inside the adsorption tower 21 was regenerated.

[0074] After the adsorption process in the adsorption tower 22 and the regeneration process in the adsorption tower 21 were completed, a pressure equalization process was carried out to transfer the gas in the adsorption tower 22 to the adsorption tower 21. The pressure equalization process was carried out by closing the on-off valves V2, V4, V5, and V6 and opening the on-off valves V8 and V9.

[0075] The adsorption process of adsorption tower 21, the regeneration process of adsorption tower 22, and the pressure equalization process were defined as one cycle, and the adsorption process of adsorption tower 22, the regeneration process of adsorption tower 21, and the pressure equalization process were defined as one cycle. A cycle of the adsorption process of adsorption tower 21, the regeneration process of adsorption tower 22, and the pressure equalization process (hereinafter, this cycle will be referred to as "cycle 1") and a cycle of the adsorption process of adsorption tower 22, the regeneration process of adsorption tower 21, and the pressure equalization process (hereinafter, this cycle will be referred to as "cycle 2") were alternately repeated for 540 seconds.

[0076] <Example 2> In Example 2, CO2 adsorption was performed by the CO2 adsorption system in the same manner as in Example 1, except that in cycles 1 and 2, the CO2-containing gas G1 was supplied at a flow rate of 10 L / min.

[0077] <Example 3> In Example 3, CO2 adsorption was performed by the CO2 adsorption system in the same manner as in Example 1, except that in cycles 1 and 2, the CO2-containing gas G1 was supplied at a flow rate of 15 L / min.

[0078] <Example 4> In Example 4, CO2 adsorption was performed by the CO2 adsorption system in the same manner as in Example 1, except that the cycle times in cycles 1 and 2 were set to 4 seconds.

[0079] <Example 5> In Example 5, CO2 adsorption was performed by the CO2 adsorption system in the same manner as in Example 1, except that the cycle times in cycles 1 and 2 were set to 6 seconds.

[0080] <Example 6> In Example 6, CO2 adsorption was performed by the CO2 adsorption system in the same manner as in Example 1, except that the cycle times in cycles 1 and 2 were set to 8 seconds.

[0081] <Example 7> In Example 7, CO2 adsorption was performed by the CO2 adsorption system in the same manner as in Example 1, except that the cycle times in cycles 1 and 2 were set to 10 seconds.

[0082] <Example 8> In Example 7, CO2 was adsorbed by the CO2 adsorption system in the same manner as in Example 1, except that the pressure of the CO2-containing gas G1 in cycles 1 and 2 was set to 150 kPa.

[0083] <Example 9> In Example 9, CO2 was adsorbed by the CO2 adsorption system in the same manner as in Example 1, except that the pressure of the CO2-containing gas G1 in cycles 1 and 2 was set to 175 kPa.

[0084] <Example 10> In Example 10, CO2 adsorption was performed by the CO2 adsorption system in the same manner as in Example 1, except that the amount of zeolite packed in the adsorption towers 21 and 22 was 130 g.

[0085] <Example 11> In Example 11, the zeolite packed in the adsorption towers 21 and 22 was prepared by crushing pellet-shaped zeolite and passing it through a sieve with an opening of 0.5 mm to 1.0 mm. Except for this, and the amount of zeolite packed was 135 g, the adsorption of CO2 was carried out using the CO2 adsorption system in the same manner as in Example 1.

[0086] <Example 12> In Example 12, the zeolite packed in the adsorption towers 21 and 22 was prepared by crushing pellet-shaped zeolite and passing it through a sieve with an opening of 0.5 mm to 1.0 mm. Except for this, and the amount of zeolite packed was 135 g, the adsorption of CO2 was carried out using the CO2 adsorption system in the same manner as in Example 2.

[0087] <Example 13> In Example 13, the zeolite packed in the adsorption towers 21 and 22 was prepared by crushing pellet-shaped zeolite and passing it through a sieve with an opening of 0.5 mm to 1.0 mm. Except for this, and the amount of zeolite packed was 135 g, the adsorption of CO2 was carried out using the CO2 adsorption system in the same manner as in Example 3.

[0088] <Example 14> In Example 14, the zeolite packed in the adsorption towers 21 and 22 was pellet-shaped MFI type zeolite (product name "890HOA", manufactured by Tosoh Corporation) that had been crushed and passed through a sieve with mesh sizes of 0.5 mm to 1.0 mm. The amount of zeolite packed was 130 g. CO2 was added to the air to increase the CO2 partial pressure in the CO2-containing gas to 0.19 kPa. Except for this, adsorption of CO2 was performed using a CO2 adsorption system in the same manner as in Example 1.

[0089] <Example 15> In Example 15, CO2 was adsorbed by the CO2 adsorption system in the same manner as in Example 14, except that the CO2 partial pressure in the CO2-containing gas G1 in cycles 1 and 2 was increased to 0.68 kPa.

[0090] <Example 16> In Example 16, CO2 was adsorbed by the CO2 adsorption system in the same manner as in Example 14, except that the CO2 partial pressure in the CO2-containing gas G1 in cycles 1 and 2 was increased to 1.35 kPa.

[0091] <Example 17> In Example 17, CO2 was adsorbed by the CO2 adsorption system in the same manner as in Example 14, except that the CO2 partial pressure in the CO2-containing gas G1 in cycles 1 and 2 was increased to 2.13 kPa.

[0092] <Example 18> In Example 18, CO2 was adsorbed by the CO2 adsorption system in the same manner as in Example 14, except that the CO2 partial pressure in the CO2-containing gas G1 in cycles 1 and 2 was increased to 3.46 kPa.

[0093] <Comparative Example 1> In Comparative Example 1, 13X beads (0.4 mm to 0.8 mm, manufactured by Wako Pure Chemical Industries, Ltd.) were used as the zeolite packed in the adsorption towers 21 and 22, and the amount of zeolite packed was 135 g, but other than this, CO2 adsorption was performed using the CO2 adsorption system in the same manner as in Example 1. The moisture adsorption rate of this zeolite in an environment of a temperature of 25°C and a relative water vapor pressure of 0.5 was 25% by weight.

[0094] <Average CO2 concentration> During operation of the CO2 adsorption systems of Examples 1 to 18 and Comparative Example 1, the CO2 concentration of the CO2-containing gas G1 flowing through the CO2-containing gas supply line 31, the CO2 concentration of the product gas G2 flowing through the product gas extraction line 32, and the CO2 concentration of the exhaust gas G4 flowing through the exhaust line 34 were each measured, and the average CO2 concentration was calculated for each.

[0095] <Average relative humidity> During operation of the CO2 adsorption systems of Examples 1 to 18 and Comparative Example 1, the relative humidity of the CO2-containing gas G1 flowing through the CO2-containing gas supply line 31, the relative humidity of the product gas G2 flowing through the product gas extraction line 32, and the relative humidity of the exhaust gas G4 flowing through the exhaust line 34 were each measured, and the average relative humidity was calculated for each.

[0096] The results are shown in Table 1. In Table 1, G1 means CO2-containing gas, G2 means product gas, and G4 means exhaust gas. [Table 1]

[0097] The results are described below. In Comparative Example 1, the moisture adsorption rate of zeolite was large, so when the CO2 partial pressure was low, CO2 could not be sufficiently adsorbed from the CO2-containing gas G1. This is thought to be because moisture was not removed from the CO2-containing gas G1 as a pretreatment, and the zeolite adsorbed moisture in the CO2-containing gas G1. In contrast, in Examples 1 to 18, the moisture adsorption rate of zeolite was 5% by weight or less under an environment of a temperature of 25°C and a relative water vapor pressure of 0.5, so when the CO2 partial pressure was low, CO2 could be sufficiently adsorbed from the CO2-containing gas G1 without removing moisture from the CO2-containing gas G1 as a pretreatment.

Claims

1. Using zeolite ２ CO in the gas ２ CO absorbs ２ 1. An adsorption system comprising: CO ２ CO in the gas ２ one or more adsorption columns packed with a zeolite that adsorbs The CO ２ CO containing gas supply ２ A gas-containing supply line; The CO ２ The CO ２ A compressor for compressing the contained gas; The CO ２ CO from contained gas ２ a product gas extraction line for extracting the product gas from which the gas has been separated; The CO ２ CO in the gas ２ A pressure control unit that controls the compressor so that the partial pressure is 0.001 kPa or more and less than 100 kPa, The water adsorption rate of the zeolite is 5% by weight or less under an environment of a temperature of 25° C. and a relative water vapor pressure of 0.

5. ２ Adsorption system.

2. 2. The CO composition according to claim 1, wherein the zeolite does not contain Al or the Si / Al atomic ratio of the zeolite is 50 or more. ２ Adsorption system.

3. The CO ２ The CO ２ 2. The CO gas supply method according to claim 1, wherein the on-off valve is controlled so that the supply time of the CO gas is 1 second or more and 120 seconds or less. ２ Adsorption system.

4. The system further comprises a regeneration gas supply line that branches off from the product gas extraction line, is connected to each of the adsorption towers, and supplies a portion of the product gas as a regeneration gas to each of the adsorption towers; a product gas flow rate regulator that is interposed in the product gas extraction line and regulates the flow rate of the product gas; and a product gas flow rate control unit that controls the product gas flow rate regulator, wherein the product gas flow rate control unit regulates the product gas and the CO ２ 2. The CO gas according to claim 1, wherein the product gas flow rate regulator is controlled so that the flow rate ratio of the product gas and the contained gas is 1:1.1 to 1:

20. ２ Adsorption system.

5. Using zeolite ２ CO in the gas ２ CO absorbs ２ 1. An adsorption method comprising the steps of: Providing one or more adsorption columns packed with zeolite; In the adsorption tower ２ CO partial pressure is 0.001 kPa or more and less than 100 kPa ２ A gas containing CO is supplied, and the CO is converted by the zeolite. ２ CO in the gas ２ and removing the product gas from the adsorption tower. The water adsorption rate of the zeolite is 5% by weight or less under an environment of a temperature of 25° C. and a relative water vapor pressure of 0.

5. ２ Adsorption method.

6. 6. The CO composition according to claim 5, wherein the zeolite does not contain Al or the Si / Al atomic ratio of the zeolite is 50 or more. ２ Adsorption method.

7. The CO ２ 6. The CO gas according to claim 5, wherein the supply time of the CO gas is 1 second or more and 120 seconds or less. ２ Adsorption method.

8. The adsorption towers are provided in two or more locations, and a part of the product gas is supplied to each of the adsorption towers as a regeneration gas, and CO is removed from the zeolite in each of the adsorption towers. ２ 6. The method of claim 5, further comprising the step of desorbing ２ Adsorption method.

9. The regeneration gas is the product gas remaining after removing a portion of the product gas and the CO ２ 9. The CO according to claim 8, wherein the flow ratio of the containing gas is 1:1.1 to 1:

20. ２ Adsorption method.

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